The present invention relates to a data communication apparatus for performing a data communication, while a wireless communication apparatus is connected to the data communication apparatus and a wireless line is utilized. More specifically, the present invention is directed to such a data communication apparatus operable in such a manner that a clock generated by the data communication apparatus gives no disturbance to the wireless communication apparatus.
Recently, since mobile communication terminals such as portable telephones are popularized and notebook type personal computers are made more compact and in lighter weight, data communications such as electronic mails and the Internet are frequently carried out by employing wireless communication lines, while wireless communication apparatuses such as portable telephones are connected to data communication apparatuses such as notebook type personal computers. Furthermore, these electronic appliances will be made more compact and in hybrid forms.
FIG. 9 schematically shows a system for executing a wireless data communication, while a wireless communication apparatus 12 is connected to the conventional data communication apparatus 11 by employing a cable, or the like.
The data communication apparatus 11 is provided with a clock generating apparatus 13 and a main CPU 14. The wireless communication apparatus 12 is provided with digital signal codec 15, frequency modulator/demodulator 16, a communication wave transceiver 17, and an antenna 18.
The clock generating apparatus 13 is constructed of an oscillator circuit by using a crystal oscillator, or electric resonance. The clock generating apparatus 13 generates an operation clock used to operate the main CPU 14. The main CPU 14 is operated at timing of the operation clock supplied from the clock generating apparatus 13. Then, the main CPU 14 outputs the transmission data to the digital signal codec 15 of the wireless communication apparatus 12, and receives the reception data from the digital signal codec 15.
The digital signal codec 15 performs a signal process operation with respect to the transmission data so as to produce a baseband signal, and supplies this baseband signal to the frequency modulator/demodulator 16. In this signal process operation, the error correction code is applied to the transmission data and the transmission data is encrypted. Also, the digital signal codec 15 performs such a process operation as a decrypting operation and an error detection/correction with respect to a baseband signal of reception data outputted from the frequency modulator/demodulator 16. The frequency modulator/demodulator 16 modulates a high frequency signal for the wireless communication based upon the baseband signal of the transmission data, and then outputs the modulated high frequency signal to the communication wave transceiver 17. Also, the frequency modulator/demodulator 16 demodulates a baseband signal from the reception signal outputted from the communication wave transceiver 17 to derive such a baseband signal, and then outputs the demodulated baseband signal to the digital signal codec 15. The communication wave transceiver 17 up-converts and amplifies the modulated high frequency signal for transmission, and then supplies the resulting high frequency signal to an antenna 18. Also, the communication wave transceiver 17 amplifies an electromagnetic wave received by the antenna 18, and down-converts the frequency of the amplified signal, and then outputs the down-converted signal to the frequency modulator/demodulator 16.
In the system arranged with employment of the above-described circuit arrangement, when data is transmitted, the main CPU 14 provided in the data communication apparatus 11 executes a data process operation with respect to this transmission data, and then transmits the data-processed transmission data to the wireless communication apparatus 12. In this data process operation, the main CPU 14 divides the transmission data and adds header/footer to the transmission data in accordance with such a data communication protocol such as TCP/IP. The digital signal codec 15 employed in the wireless communication apparatus 12 executes a signal process operation with respect to the data sent from the data communication apparatus 11 so as to produce a baseband signal. Then, the digital signal codec 15 transmits the produced baseband signal to the frequency modulator/demodulator 16. In this signal process operation, the digital signal codec 15 applies an error correction code to the sent data and encrypts the sent data. Then, the frequency modulator/demodulator 16 modulates a high frequency signal for a wireless communication by using the baseband signal, and the communication wave transceiver 17 up-converts the frequency of the modulated high frequency signal and amplifies the up-converted high frequency signal. Then, this communication wave transceiver 17 radiates the amplified high frequency signal from the antenna 18 to the air space.
When data is received, the system is operated in a manner opposite to the above-explained transmission manner. That is, a baseband signal is derived from an electromagnetic wave received by the antenna 18 by way of the communication wave transceiver 17 and the frequency modulator/demodulator 16. The baseband signal is processed by the digital signal codec 15 by executing the decrypting operation, the error detecting operation, and the error correction operation. As a result, such a signal which has been processed in accordance with the data communication protocol such as TCP/IP is outputted. Then, this resulting signal is transmitted via a cable, a connector, and the like to the data communication apparatus 11. The main CPU 14 of the data communication apparatus 11 removes the header and the footer, which are applied in accordance with the TCP/IP protocol, and combines the removed data with each other to reproduce the reception data.
The data communication apparatus contains the clock generating apparatus, such as an oscillator circuit using the crystal oscillator or the electric resonance, in order to operate the CPU. From such a clock generating apparatus, harmonic content having such frequencies higher than the desirable frequency of the clock by 2 times, 3 times, 4 times, - - - , are derived in addition to the clock having the desirable frequency. These harmonic content are referred to as “multiplied wave noise”, and are radiated as disturbance waves (interference waves) from the data communication apparatus to the air space.
The multiplied wave noise generated from the clock generating apparatus provided inside the data communication apparatus is propagated through the air space, and may give disturbances, or interference to electronic appliances such as televisions and radios located around this data communication apparatus. In particular, as to such a data communication apparatus operated in the mode that a portable telephone is connected to this data communication apparatus so as to execute a wireless data communication, the wireless communication apparatus such as the portable telephone is positioned in the vicinity of the data communication apparatus, or is manufactured in an integral form with this data communication apparatus. As a result, the wireless communication apparatus easily receives the disturbance waves caused by the multiplied wave noise. Unfortunately, in such a case that the multiplied wave noise is made coincident with the wireless communication frequency, this may give adverse influences to the wireless communications, for instance, the reception sensitivity would be deteriorated, the data error rate would be deteriorated, and the data communication speed would be lowered.
FIG. 10 graphically represents a characteristic in which higher order waves (namely, harmonic content multiplied by “n”) of multiplied wave noise give an adverse influence to a reception frequency range of a wireless communication apparatus.
To solve this problem, since the clock generating apparatus is covered by employing a metal case so as to be electrically shielded, the radiated multiplexed wave noise is reduced. Also, since the spatial distance between the data communication apparatus and the wireless communication apparatus is separated from each other by employing the cable, the adverse influence caused by the multiplexed wave noise can be hardly received. However, the shield case may disturb the light weight of the data communication apparatus. Also, if the conventional method for separating the distances among the apparatuses by employing the cables, then the design policy for making the respective apparatuses compact has no meaning.